In recent years, as the processing speed of a computer has increased, it has been required that a large amount of data be transferred at a higher speed among a plurality of computers. In order to achieve such data transfer, for example, an electrical interconnection having been conventionally used for connecting elements in a high-end server tends to be replaced with an optical interconnection which operates at a higher speed.
In optical communications utilizing the optical interconnections, semiconductor lasers are often used. In particular, a surface emitting laser is employed in many cases rather than an edge emitting laser used in long-distance communications because the surface emitting laser is less expensive and consumes less power than the edge-emitting laser.
In order to meet the demand for such surface emitting lasers, companies in this field have been actively conducting research and development on improvement in a structure and manufacturing method of a surface emitting laser. As a result, for example, the following patent application publications have been issued as background arts.
An object of the invention according to Japanese Patent Application Laid-open Publication No. Hei 11-97796, is to facilitate the manufacture of a GaN-based group III-V nitride surface emitting laser. Disclosed are a group III-V compound semiconductor surface emitting laser and a manufacturing method thereof. This group III-V compound semiconductor surface emitting laser includes a cavity intervening between a pair of distributed Bragg reflectors on a semiconductor substrate. In this surface emitting laser, each of the distributed Bragg reflectors is formed by alternately stacking air layers and material layers each having a refractive index higher than that of the air layers.
An object of the invention according to Japanese Patent Application Laid-open Publication No. 2000-353858 is to provide a highly-reliable surface emitting laser with small total thickness, which is capable of oscillating at long wavelength and of a single lateral mode operation, and which is easy to manufacture. Disclosed are a surface emitting laser and a manufacturing method thereof. This surface emitting laser includes an upper multilayered semiconductor layer and a lower multilayered semiconductor layer, respectively over and under an active layer. In this surface emitting laser, the upper multilayered semiconductor layer and the lower upper multilayered semiconductor layer have a DBR structure of air gap layers/semiconductor layers and a DBR structure of air gap layers/semiconductor layers, respectively.
In Japanese Patent Application Laid-open Publication No. 2001-358403, disclosed is a surface emitting laser making it possible to efficiently excite a long-wavelength surface emitting laser by means of an optical pump, and also to monolithically manufacture DBRs each having a high reflectivity, and an active layer, on an InP substrate, without fusion bonding. In this surface emitting laser, when the refractive indices of semiconductors having the lowest refractive index and the highest refractive index among semiconductors composing the semiconductor distributed Bragg reflector are represented respectively by nD1 and nD2, and concurrently the refractive index of a carrier confinement layer is represented by nS, a relationship nD1<nS<nD2 is held.
As has been described above, the surface emitting laser has the advantages of being less expensive and of consuming lower power than the edge emitting laser. However, the surface emitting laser has a problem of having a life which is as long as or shorter than about one tenth of that of the edge emitting laser. In a case where a surface emitting laser is used for a connection between computer systems each simultaneously using a large number of elements, this problem becomes a particularly serious problem in terms of reliability of the systems.